Tappets are used in valve trains and pump drives for converting in cooperation with at least one cam of a camshaft or with a pump drive shaft, a rotational movement of said shaft into a translational movement of a valve or of a pump piston. In the case of a valve train of an internal combustion engine with a bottom camshaft, the tappet is further in contact through a tappet pushrod and a rocker arm with an associated gas exchange valve, while in the case of an overhead camshaft, a tappet mostly configured as a cup tappet, is disposed directly between cam and gas exchange valve. In the case of a pump drive, too, the tappet is likewise usually arranged directly between a cam of the pump drive shaft and the respective pump piston.
In addition, for reducing friction, frequently, either a vaulted running surface is configured on an outer body of the tappet, or the outer body comprises a running roller that is mounted for rotation on the outer body and runs along the cam of the camshaft or on the pump drive shaft. In order to assure a permanent correct orientation of the running surface or running roller relative to the respective cam and thus also to prevent an undesired rotation of the tappet, the tappet is usually provided with an anti-rotation element through which the tappet is fixed in peripheral direction and runs along a lift axis in a guide of a surrounding component, for instance the cylinder head of the internal combustion engine or in a pump housing. Frequently, this anti-rotation element is pressed into a corresponding through-opening on a wall region of the outer body.
However, the light-weight structure with small wall thicknesses in the wall region as well as heat treatments and coatings lead partially to occurrence of cracks in the region of the through-opening when the anti-rotation element is being pressed into the through-opening. For avoiding such cracks, it is necessary to respect narrow tolerances in making the through-opening and also during the manufacture of the associated anti-rotation element, all this resulting in a corresponding technical complexity and higher expenses. By reason of this fact, an anti-rotation element is sometimes also applied to the outer body by other methods.
DE 10 2004 036 106 A1 discloses a tappet in the form of a cup tappet for a valve train of an internal combustion engine. This tappet comprises a hollow cylindrical outer body on whose front end a counter running surface for a cam of the valve train is configured, while the outer body comprises on a wall region, a window-type through-opening. An anti-rotation element with a mushroom-shaped cross-section is received in this through-opening and is positioned with the region of a head comprising support surfaces on an outer diameter of the wall region, while the anti-rotation element is inserted through the through-opening with a shank starting from the head and is fixed with the shank in the through-opening. One possible method for this fixing proposed by DE 10 2004 036 106 A1 is to weld the shank of the anti-rotation element to the through-opening.